Upgrade Xen Headers

[garethodickin]

We'd like to upgrade drivers/xen/xenheaders/ to be compatible with v4.20. Our immediate issue is XEN_SYSCTL_scheduler_op hypercall rejected due to version mismatch, but any other unstable interface usage (domctl, etc.) will hit the same version mismatch problem.
For reference, here are impacted headers and used-by xen drivers:

Header	Used by
xen/xen.h	All
xen/grant_table.h	xengnttab
xen/memory.h	xengnttab, plat/xen
xen/event_channel.h	plat/xen
xen/io/ring.h	netfront, blkfront, 9pfront
xen/io/netif.h	netfront
xen/io/blkif.h	blkfront
xen/io/9pfs.h	9pfront
xen/io/console.h	xencons
xen/io/xenbus.h, xs_wire.h	xenbus
xen/sched.h	plat/xen
xen/hvm/hvm_op.h, params.h	plat/xen

[sookyung-ahn]

The issue is that XEN_SYSCTL_INTERFACE_VERSION in Unikraft is outdated. Xen since 4.17 uses 0x15, but Unikraft still uses 0x10.
XEN_SYSCTL_INTERFACE_VERSION is defined in sysctl.h.

[michpappas]

I see no problem with that. Notice that there have been some changes to the Xen headers in 37be465, 54ce152 and possibly during import (it's unclear to me from 00d0274 whether the headers were dropped verbatim). If that increases maintenance effort you may consider introducing a header that adapts upstream headers to Unikraft.

[sookyung-ahn]

The changes in 37be465 and 54ce152 are mostly comment-only. The only active code changes are in ring.h, where upstream Xen symbols are replaced with Unikraft equivalents:

Xen (a02bb8da93)	Unikraft	Where / Note
rdtsc()	uk_arch_rdtsc()	save.h (comment only)
PAGE_SIZE	UK_PAGING_PAGE_SIZE	blkif.h, fbif.h, ring.h (comments only)
mb()	uk_arch_mb()	ring.h (active code)
rmb()	uk_arch_rmb()	ring.h (active code)
wmb()	uk_arch_wmb()	ring.h (active code)

As for 00d0274, it only relocated the headers from plat/xen/include/xen to drivers/xen/xenheaders/include/xen with no content changes.

[michpappas]

That's right. The question is more about whether upstream Xen headers should be drop-in. IMO ideally they should be (as much as possible) to minimize the maintenance effort during upgrades, but that's something that can also be deferred to a separate task.